THE SPLEEN IX MARSUPIALS. 



A new feature becomes added which can be effectively 

 studied throughout the Primates, viz. the inclusion by 

 great omentum first of the mesocolon and later of the 

 distal colon — the pancreas now being a dorsal organ. 

 This inclusion or fusion begins from right to left, and the 

 importance of the mesial fold previously mentioned, 

 between the colon and pyloric region, is seen. Early 

 phases of this can be studied in Macropus. In a young 

 Baboon (Oatarrhina ) (page 154), the ik lieno-mesocolic v 

 is simply a fold between the spleen and the upper part of 

 the kidney, i.e. it is atrophying, and the ridge on the inner 

 surface of the posterior angle or process has almost gone. 

 The lower part of the renal and the colic surfaces are be- 

 coming continuous with the " intermediate'' angle be- 

 coming evident. Here, however, the colon is not fixed, 

 but the mesocolon at its commencement is partially 

 applied to the great omentum. The colic surface is not, 

 as in the human spleen, encroached on by the stomach, i.e. 

 the relationship of colon to spleen is not limited as in the 

 human, and the gastro-splenic omentum goes almost to 

 the tip of the anterior process. In a young Orang Utang, 

 however (p. 154 ), the color is fixed dorsally. It is included 

 (secondarily) in the lesser sac by the great omentum, 

 and has only a limited relation to the spleen. The anterior 

 portion of the colic surface is encroached on by the 

 stomach as in the human spleen. Thus, with its fixation 

 the colon comes into relation with a limited area of spleen 

 only, though previously related to the whole colic surface. 

 As to whether the stomach will encroach on the colic sur- 

 face depends on the atrophy of the right or anterior part 

 of the gastro-splenic omentum. With dorsal fixation of 

 the spleen the membrane further atrophies and the 

 stomach encroaches as in the human spleen. But where 

 there is mobility, i.e. not good dorsal fixation, the anterior 

 part of the lower surface is colic not gastric. Thus we 



156 



